The present invention relates to an improvement of a switch for an on-vehicle horn.
More particularly, it is directed to the provision of a membrane switch for an on-vehicle horn that does not malfunction, exhibits negligible variation operating force, and is excellent in durability.
Conventionally, a switch for an on-vehicle horn, especially a membrane switch, basically comprises, as shown in FIG. 4, a pair of electrode plates 12 having an insulating film 13 placed thereon (for example, a polyester film with a conducting metal such as aluminum evaporated thereon, or copper foil) and a spacer (for example, a polyester film) 11 interposed between the electrode plates at a predetermined distance 14, in which connection terminals 15 for lead wires or the like are attached to the electrode plates 12 and electrically connected to the vehicle body side.
Known examples of such membrane switches include: (i) a type in which the spacer is made of foam plastics (U.S. Pat. No. 4,882,460); (ii) a type in which the spacer is provided in the interior surface of the outer cover (U.S. Pat. No. 5,265,904); and (iii) a type in which the spacer is constituted of projections (dots) 16 formed on an electrode plate 12 by printing with a thermosetting resin ink as shown in FIG. 5.
FIG. 4 is a sectional view showing a typical structure of a membrane switch.
FIG. 5 is a schematic diagram showing the structure of a spacer comprising a conventional membrane switch.
Referring to FIGS. 4 and 5, reference numeral 11 denotes a spacer, 12 denotes an electrode plate, 13 denotes an insulating film (base plate), 14 denotes a gap, 15 denotes a connection terminal, and 16 denotes a printed-dot spacer.
(i) When the spacer is made of foam material, there is such a danger that its height of the spacer is gradually reduced by repeated load applied thereon and its operating force is thereby changed and therefore results in the drawback of deficient durability.
(ii) When the spacer is provided on the surface of the outer cover, its operating force varies with the position of the push given thereon because the distances between the projections, serving as the spacer, are large.
(iii) When the spacer is provided with printed projections:
(A) variations in the operating force are caused by variations in the height of the dotted objects;
(B) a malfunction tends to occur such that the switch becomes contacted, while it is expected to be separated, because the printed dots cannot be made sufficiently high; and
(C) the fabrication process becomes complicated because, in addition to the formation of the printed dots, provision of an adhesive layer on the circumference of the electrode is required to laminate two electrodes.
The inventors, after various investigations of the above mentioned problems, found that a membrane switch which has no malfunction, small variation in the operating force, and is excellent in durability can be provided by giving, in a membrane switch, a specific thickness to the spacer and a specific size to the through hole in the spacer to thereby keep the operating force within a predetermined range and, thus, completed the present invention.
Namely, the invention:
(1) provides a membrane switch comprising a pair of conductive electrode plates confronting each other and a spacer separating the same, wherein the operating force required to operate the switch by pressing it with a round rod having a hemispherical tip with a radius of curvature of 5 mm is within the range of 0.03 to 0.2 kg; and
(2) it is also characterized in that the spacer is in the form of a film, the film has through holes, and the aperture ratio of the through holes is 50% or above. It further
(3) provides a method of fabricating the membrane switch mentioned in (1) or (2) in which the operating force is kept within the range of 0.03 to 0.2 kg by setting the thickness of the spacer and the size of the through hole in the spacer to predetermined values;
(4) it is also characterized in that the thickness of the spacer is 20-150 xcexcm and the size of one through hole in the spacer is 2-10 mm square; and
(5) it is also characterized in that an insulating film with a predetermined thickness and having predetermined through holes made therein is used as the spacer.
Referring to the drawings, the invention is described below in concrete terms.
The present invention basically is a membrane switch comprising a pair of conducting electrode plates disposed confronting each other and a spacer inserted therebetween, wherein the operating force required to operate the membrane switch by pressing it with a round rod with a hemispherical tip having a radius of curvature of 5 mm is within the range of 0.03 to 0.2 kg, or preferably within the range of 0.05 to 0.15 kg.
As the spacer, it is preferable to use an insulating film with specific through holes made therein.
In this case, when the operating force is less than 0.03 kg, a malfunction tends to occur such that the conducting electrode plates are still electrically in contact to each other even if the switch is released to be off. When it exceeds 0.2 kg, a malfunction tends to occur such that the line is not conducting even if the switch is pressed to be on. Either case is not desirable.
While the portion other than the through holes of the insulating film serves as the spacer, it is preferred that the pair of confronting conducting electrode plates are insulated from each other by the spacer when the membrane switch is not pressed and they become definitely conducting when the membrane switch is pressed to blow the horn. However, the spacer, especially the shape of the through hole, is not limited to the shape shown in the figure, but that in a circular, elliptical, polygonal, and other shape can be suitably used.
In the invention, by setting the thickness of the spacer and the size of the through hole to predetermined values, a membrane switch having an operating force of 0.03-0.2 kg, without no malfunction and excellent in durability can be provided.
Accordingly, to keep the operating force within 0.03-0.2 kg, it is preferred that the thickness of the spacer be set to 20-150 xcexcm, or more preferably to 25-125 xcexcm, and the size of the through hole, when it is for example of a square shape, be set to 2-10 mm square, or more preferably to 2.5-8 mm square.
The operating force can be decreased according to enlarging the aperture ratio of the through hole in the spacer.
However, insofar that the spacer must maintain insulation between electrode plates, portions other than the through holes must be left. Therefore, an aperture ratio of 50% to 80% is preferable. The pitch distance of the through holes is normally 0.5-2.0 mm, or preferably 1.0-1.5 mm.